Abstract [en]

A class of capability indices, containing the indices Cp, Cpk, Cpm, and Cpmk, has earlier been defined by the author for the case of two-sided specification intervals. By varying the parameters of the class various indices with suitable properties can be obtained. Under the assumption of normality new and simplified expressions of the distribution and the moments of the class of the estimated indices are provided when the target value equals the mid-point of the specification interval. It is shown that the cumulative distribution function can be expressed using only the central χ2-distribution and the normal distribution, which increases the utility of the class of indices.